It was, perhaps, shocking enough when the authorities announced last week that after 12 years of fruitless investigation they had arrested a man in connection with the gruesome murder of a 19-year-old Brooklyn man whose expertly dismembered body was discovered spread in plastic bags in a subway station and a trash recycling plant.

But in making the announcement on Wednesday afternoon, the police and prosecutors revealed another tantalizing tidbit: The suspect had also been charged with a second cold-case murder — that of a 17-year-old girl whose remains had been found in an alley inside laundry bags a year before the young man’s body was discovered.

Unlike the killing of Rashawn Brazell, which garnered widespread coverage in the media, including three episodes of “America’s Most Wanted” on television, the long-mysterious earlier death went essentially unmentioned for more than a decade. The naked body of the girl, Sharabia Thomas, had been discovered, folded in half and stuffed inside the bags, in Bushwick, Brooklyn, 13 years ago, bruised and bearing marks suggesting that she had been tied up before she died.

Prosecutors said Ms. Thomas had last been seen by her family on Feb. 11, 2004, as she left her home on Gates Avenue and headed to class at the EBC High School in Bushwick. Shortly after 4 p.m. that day, the police found her body. Though investigators determined that the cause of death was choking and found no signs of sexual assault, prosecutors said they had initially been unable to identify the body.

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The case of Ms. Thomas’s murder had gone cold, but last year detectives caught an unexpected break.CreditBrooklyn District Attorney's Office

Within a day of Ms. Thomas’s disappearance, her family reported her missing, but it took four more days, prosecutors said, for investigators to connect that report with the body they had found in the alley off Palmetto Street, a few blocks from the Thomas family home. And for the next 12 years the case remained unsolved, eventually landing in the laps of Detectives Evelin Gutierrez and Jason Palamara of the New York Police Department’s Cold Case Squad.

It was only late last spring that the detectives caught a break, one involving the sudden resolution of a third cold-case killing in the borough. In June, the Brooklyn district attorney’s office announced that it was charging a Brooklyn man, who was at that point imprisoned in the Caribbean, in the murder of Chanel Petro-Nixon.

Ms. Petro-Nixon, 16, disappeared on Father’s Day in 2006 while on her way to a job interview at an Applebee’s restaurant, not far from her home in Bedford-Stuyvesant. Four days later, her body was discovered, partly clothed and strangled, in a trash bag on the street outside her building.

The suspect, Veron Primus, was in custody on the island of St. Vincent in an unrelated murder case. Within days of his being charged, the police and prosecutors renewed their efforts to investigate other unsolved killings of young Brooklyn women for links to him.

As part of their investigation, the authorities tested clippings from Ms. Thomas’s fingernails, which had been saved as evidence for more than a decade, prosecutors said. The fingernails contained a sample of DNA other than Ms. Thomas’s. When investigators ran that sample through a national database, they got a match, prosecutors said, not to Mr. Primus but to another man: Kwauhuru Govan, a onetime security camera technician who had once lived only blocks from Ms. Thomas.

The match was made because Mr. Govan was already in prison: in Florida, serving a three-year sentence for robbing a Polk County deli with a gun, court records show. Detectives from the Cold Case Squad traveled to Florida to interview him, police officials said. And while it remains unclear what Mr. Govan said, prosecutors charged him in November with killing Ms. Thomas.

A version of this article appears in print on , on Page A17 of the New York edition with the headline: A Dozen Years, 3 Cold Cases and an Arrest in Brooklyn. Order Reprints | Today’s Paper | Subscribe